replace deprecated "app" label selector by "app.kubernetes.io/name" in

documents and examples

examples/example-app/example-app.yaml

@@ -7,7 +7,7 @@ metadata:
   namespace: default
 spec:
   selector:
-    app: example-app
+    app.kubernetes.io/name: example-app
   ports:
   - name: web
     protocol: TCP
@@ -22,17 +22,17 @@ metadata:
 spec:
   selector:
     matchLabels:
-      app: example-app
+      app.kubernetes.io/name: example-app
       version: 1.1.3
   replicas: 4
   template:
     metadata:
       labels:
-        app: example-app
+        app.kubernetes.io/name: example-app
         version: 1.1.3
     spec:
       containers:
-      - name: example-app 
+      - name: example-app
         image: quay.io/fabxc/prometheus_demo_service
         ports:
         - name: web